The present invention relates to optical transmission equipment and more particularly, to a wavelength gain characteristic shift slope filter, optical transmission equipment and optical transmission method, which are suitable for wavelength division multiplexing.
In order to cope with rapid increase of traffic involved by rapid spread of the Internet, dense wavelength division multiplexing (DWDM) has been implemented in North America. The implementation of the DWDM is due to the fact that an optical amplifier for use in collective amplification of wavelength division multiplexing light has an amplification band. However, the gain of the optical amplifier depends on wavelength and further the wavelength dependency also varies depending on its input level. For this reason, the current wavelength division multiplexing cannot use the full amplification band of the:optical amplifier and can use only a band called xe2x80x9cred bandxe2x80x9d having a relatively flat gain wavelength dependency.
In this connection, the articles associated with the invention of the present application are U.S. Pat. Nos. 5,675,432 and 5,987,200 and U.S. application Ser. No. 09/191,051 (JP-A-11-150526) now U.S. Pat. No. 6,400,475, the description of the articles being hereby incorporated by reference. Described in the U.S. Pat. No. 5,987,200 is a multiplexing/demultiplexing device of a narrow-band Bragg grating type which can change add/drop wavelengths by changing the temperature of a fiber grating.
It is an object of the present invention to implement a wavelength gain characteristic shift slope filter which dynamically equalizes its gain according to its input level. Another object of the present invention is to provide optical transmission equipment which is suitable for wavelength division multiplexing. A yet object of the present invention is to provide an optical transmission method which is suitable for wavelength division multiplexing.
The above objects can be attained by providing a wavelength gain characteristic shift slope filter which includes a filter section for obtaining filter characteristics associated with wavelength gain characteristics for a plurality of input levels thereof by changing the temperature of the optical amplifier and which also includes a Peltier element for controlling the temperature of the filter section. The above objects can be attained also by providing optical transmission equipment which includes wavelength gain characteristic shift slope filters for compensating for wavelength gain characteristics according to the input levels, optical gain adjusters, and optical amplifiers for amplifying optical signals having a plurality of wavelengths. The above objects are attained also by providing optical transmission equipment wherein an amplification band is divided with wavelengths providing inflection points to a wavelength gain characteristic of at least an impurity-doped fiber to adjust its gain for each of the divided wavelength bands.